In order to generate primary color signals for representing an image, a planar array of filtered charge-coupled devices (CCD) is placed in image-capturing devices such as a digital camera and a scanner. The planar array of CCDs also generates information related to the light intensity of an original image. For example, Japanese Patent Laid Publication Hei 2-128591 discloses the use of four color filters with the CCDs for first generating a first set of color signals each representing Magenta, Cyan, Yellow and Green and then converting them to a second set of signals representing Red, Green and Blue. This type of approach, however, tend to cause moire and undesirable colors on edges due to an arrangement of the color filters and interpolation.
To illustrate the above problem, referring to FIG. 1, an exemplary 3×3 color filtered CCDs are shown with solid lines. The color filter of the CCDs is indicated by R for red, G for green and B for Blue. These exemplary 3×3 CCDs arranged to include three rows of a top row having (G, R, G), a middle row having (B, G, B) and a bottom row having (G, R, G). The intensity signals generated by the above CCDs are interpolated by a set of interpolation filters such as shown in FIG. 2 in order to generate a set of RGB primary color signals. For example, the R signal is generated by multiplying a coefficient ½ to the corresponding R intensity signal which is located in the middle of the top and bottom rows and then by adding them. The G signal is generated by multiplying 1 to the corresponding G intensity signal which is located in the middle of the middle row. Lastly, the B signal is generated by multiplying a coefficient ½ to the corresponding B intensity signal which is located in the left and right of the middle row and then by adding them.
Now referring to FIGS. 3A and 3B, undesirable results in the RGB signals emerge when the same color filtered CCDs process an image containing abrupt intensity changes or abrupt gradients such as stripes. FIG. 3A illustrates that the above color filtered CCDs process horizontal 2-pixel-cycle black-and-white stripes. The top and bottom row CCDs process white image portions while the middle row CCD processes a black image portion. Using the same interpolation filters as shown in FIG. 2, the R signal is generated by multiplying a coefficient ½ to the corresponding R intensity signal having the value of 255 which is located in the middle of the top and bottom rows and then by adding them. The G signal is generated by multiplying 1 to the corresponding G intensity signal having the value of 0 which is located in the middle of the middle row. Lastly, the B signal is generated by multiplying a coefficient ½ to the corresponding B intensity signal having the value of 0 which is located in the left and right of the middle row and then by adding them. Thus, the ROB signals have the value of (255, 0, 0). This means that the color of the black-and-white stripes is now undesirably represented by red.
Referring to FIG. 3B, the above color filtered CCDs process the same frequency black-and-white horizontal stripes. However, the top and bottom row CCDs now process black image portions while the middle row CCD processes a white image portion. Using the same interpolation filters as shown in FIG. 2, the R signal is generated by multiplying a coefficient V2 to the corresponding R intensity signal having the value of 0 which is located in the middle of the top and bottom rows and then by adding them. The G signal is generated by multiplying 1 to the corresponding G intensity signal having the value of 255 which is located in the middle of the middle row. Lastly, the B signal is generated by multiplying a coefficient ½ to the corresponding B intensity signal having the value of 255 which is located in the left and right of the middle row and then by adding them. Thus, the RGB signals have the value of (0, 255, 255). This means that the color of the black-and-white stripes is now undesirably represented by cyan.
As described in the above, the image processing method and system remains to be improved for substantially reducing the undesirable effects such as colored edges on black-and-white stripes as well as moire problems associated with abrupt gradients in the color images.